1. Field of the Invention
The invention relates, in general, to a method for sterilizing medical instruments with steam and, in particular, to a sterilization container useful for flash sterilization and gas plasma sterilization, which includes a filter that permits maximum steam or gas sterilant penetration and prevents microorganisms and dust from entering.
2. Description of Related Art
Steam sterilization is a common method used for the sterilization of items, especially medical instruments by processing the items in an autoclave and exposing them to high-pressure steam. This method requires the wrapping of individual items, heating the items with steam and then waiting for a drying/cooling period. Often during surgical procedures commonly used instruments need to be quickly sterilized after use or inadvertent contamination. Under such circumstances the standard autoclave method would take too long. An alternative sterilization method which can be used under these circumstances, is known as flash sterilization. In flash sterilization metal instruments are not wrapped but are heated directly by the steam allowing sterilization in a reduced period of time. One drawback to the use of flash sterilization is the lack of a drying period. When the items are still moist and hot from sterilization. microorganisms and dust can contaminate the items when they are transported from the autoclave/sterilizer. Nevertheless, flash sterilization results in reduced exposure time.
One common design for containers for flash sterilization is described in U.S. Pat. Nos. 5,097,865 and 4,748,003. Such containers use valves which require greater than atmospheric pressures to open the valves and allow the high-pressure steam to enter the container but are closed under normal pressure conditions. This approach has a number of disadvantages. Such containers must be opened to allow the steam to escape, thus breaking the sterile field. Even if kept sealed, these containers cannot maintain the sterile field for longer than 24 hours. Also, the high temperature, high pressure valves needed for this method are very complex and very expensive. In addition, such containers do not provide an indication as to whether or not the valve properly functioned to allow the high pressure steam to enter the container.
The present invention facilitates the use of flash sterilization while retaining the advantage of standard autoclave sterilization by maintaining the sterility of the items in the sterilization container. Instead of a costly, complicated valve system the present invention uses a passive filter system which is capable of allowing steam to enter and exit the container and still keep microorganisms and dust out, maintaining the sterile field in the container for long term storage. The present invention, especially in the mid-size container, provides the additional advantage of reducing the time required for steam sterilization.
In addition to flash steam sterilization the industry is beginning to use gas plasma as an alternative. One commercially available gas plasma system is sold as STERRAD(copyright) by Advanced Sterilization Products, a division of the Johnson and Johnson Company. Gas plasma has known advantages over steam sterilization, including sterilizing at a lower temperature than required for steam sterilization, which is beneficial when sterilizing temperature-sensitive devices. However, it has been learned that frequently the sterilizing gas plasma does not reach all important surfaces on the inside of the sterilization container, especially where long tubular instruments or cables are contained. Accordingly, there are believed to be very few, if any, sterilization containers approved for use with gas plasma, especially in the mid-size range. Clearly a technique is missing in the prior art to guarantee satisfactory circulation of gas plasma within a sterilization container, especially where it is critical to reach the edges and corners of the interior of the sterilization container and to penetrate internal components such as laparascopic guides and tubing. The present invention, however, maintains its efficacy when utilized with gas plasma as the sterilant.
Briefly described, the invention comprises a sterilization container and a flash sterilization method for sterilizing items, which allow for extended, sterile storage of the sterilized items. The flash sterilization method uses a sterilization container having a pan, a cover and one or more filters for preventing dust and microorganisms from entering the container and contaminating the sterilized items while still allowing steam or gas plasma in and out of the container during the sterilization process. These containers can be used in the flash sterilization process commonly used in surgical theaters. The filter can be permanently mounted in the container or can be removable for replacement with new or different types of filters. Removable filters will allow for the retrofitting of currently used containers with the filters so that new containers do not need to be purchased to take advantage of the filtered flash sterilization method of the present invention. The filter can be removably attached to the container, manufactured as an integral part of the container, or incorporated into a self-contained removable filter unit.
Another aspect of the present invention comprises a novel filter retainer used for attaching a filter to the sterilization container. The filter retainer has a plurality of steam penetration holes which can be of various sizes and shapes allowing sufficient steam to enter the container. The filter retainer also comprises one or more gaskets for maintaining a seal between the filter retainer and the sterilization container as well as a locking means for removably attaching the retainer to the container.
Another alternative embodiment of the invention provides for a single set of vent holes in the center of the lid, or cover, of the container and two sets of vent holes, arranged in a circular fashion, located in the base of the pan or bottom of the container. The second and third sets of vent holes in the base are located on opposite sides of the minor axis center line of the base in such a way that they do not overlap. Gas plasma passing through the first set of vent holes in the lid is then forced to travel to the extremes of the container in order to be exhausted thereby guaranteeing that all parts of the tray or sterilizable instruments on the inside come into contact with the gas plasma as well as the edges and corners and interior of the container.
According to yet another embodiment of the invention, a pair of vent means, comprising a first and fourth set, are located in the lid in a manner similar to the way the second and third set of vent holes are located in the base. This also helps to guarantee thorough circulation of the gas plasma within the container. These two improvements are especially suited for use with mid-size sterilizable containers that employ gas plasma as the sterilizing agent. This invention, however, enhances the efficacy of all methods of sterilization, including steam sterilization and gas plasma sterilization. The first, second, third and fourth sets of vent holes are preferably each arranged in four concentric circles having the holes on their circumference. Other alternative symmetrical patterns, like square, would also be acceptable. The keeper plate on the bottom of the container preferably includes a similar set of holes, but offset so that there can be no xe2x80x9cstrikethroughxe2x80x9d of sharp objects through the filter underneath the series of vent holes but above the keeper plate.
These and other features of the invention may be more fully understood by reference to the following drawings.